In U.S. Pat. No. 5,698,250 of Gary R. DelDuca et al., which is assigned to Tenneco Packaging Inc., a "modified atmospheric package" was claimed. This package contained " . . . an oxygen scavenger activated with an activating agent . . . . " According to the patentees, the oxygen scavenger is necessary because "Low-level oxygen systems relying upon evacuation techniques to diminish oxygen levels suffer from several disadvantages . . . the evacuation techniques render it difficult to remove any oxygen within a previously wrapped package such as an overwrapped meat tray . . . . The trapped oxygen raises the residual oxygen level in the package and can also cause billowing and subsequent damage to the package during evacuation" (see lines 3-15 of column 2 of this patent). The entire disclosure of this patent is hereby incorporated by reference into this specification. Furthermore, each of the prior art references cited during the prosecution of this patent are also hereby incorporated by reference into this specification.
The "modified atmospheric package" claimed in U.S. Pat. No. 5,698,250 includes a tray which, according to lines 27-31 of column 3 of the patent, " . . . is substantially composed of polystyrene foam and has a thickness ranging from about 100 mils to about 300 mils." According to lines 22-25 of column 3 of this patent, this tray " . . . is substantially permeable to oxygen . . . ."
U.S. Pat. No. 5,698,250 was based upon an application (U.S. Ser. No. 08/627,137) which was filed on Apr. 3, 1996. Thereafter, on Dec. 13, 1996, Gary R. DelDuca et al. filed another patent application (U.S. Ser. No. 08/763,719) which issued as U.S. Pat. No. 5,811,142 on Sep. 22, 1998; the entire disclosure of which (and all of the references cited therein) are hereby incorporated by reference into this specification. In this patent, the "tray 16" is also described as being " . . . substantially permeable to oxygen . . . ," and the "modified atmosphere package" claimed also requires the presence of an " . . . oxygen scavenger . . . ."
A third patent application (U.S. Ser. No. 08/856,448) was filed by Gary DelDuca et al. on May 14, 1997; it was referred to in International Publication Number WO 98/51168, the entire disclosure of which (and all of the prior art references cited therein) is hereby incorporated by reference into this specification. This patent application claims an oxygen scavenging package comprising an iron-based oxygen absorber and an oxygen uptake accelerator. The "oxygen scavenging packet 10" contains elemental iron, and it is preferably injected with a dilute solution of acetic acid to catalyze the oxidation reaction of iron. The use of this oxygen scavenger is expensive, often representing up to about 50 percent of the total cost of the entire "modified atmosphere package"; and it presents a risk of contamination of the meat disposed in the package by either the elemental iron, ferrous oxide, ferric oxide, acetic acid, and/or reaction products thereof. According to Nick H. Proctor et al.'s "Chemical Hazards of the Workplace" (Van Nostrand Reinhold, New York, 1988), acetic acid vapor " . . . is a severe irritant of the eyes, mucous membranes, and skin . . . " (see page 47), and iron oxide fume or dust, if inhaled, " . . . causes a benign pneumoconiosis (siderosis) . . . " (page 287). In the litigious society in which we live, the use of such oxygen scavenger package not only substantially increases the cost of the "modified atmosphere package" but also increases the likelihood of product liability litigation.
It would be desirable to produce a "modified atmosphere package" which did not require the presence of an expensive and potentially dangerous oxygen scavenger to prevent spoilage of the meat packed therein. Unfortunately, when the system of the DelDuca patents is used without the oxygen scavenger, the oxygen levels within the system are high enough to cause the meat to irreversibly brown (due to the formation of metmyoglobin), thereby rendering the meat unsaleable.
It is an object of this invention to provide a packaging system for preserving perishable items (such as meat) which does not require the use of an oxygen scavenger